There are pipes with square or rectangular cross sectional shape rather than more common circular shape. Moreover, a part of the walls can be made of different materials or have different wall thicknesses. To estimate pressure wave propagation in such a channel, we examined water hammer phenomenon and measured wave speeds in rectangular tubes assembled with different wall materials and thicknesses by strain gages and pressure transducers. We newly proposed theoretical wave speeds based on the classical theory and the junction conditions of two walls: fixed, simply supported, and mixed supported. Circumferential strains on the wall can be estimated from the different forms derived by the different junction conditions. We confirmed that theoretical predictions with the simply supported conditions agreed with experimental wave speed in compound tubes, while wave speeds in ready-made square tubes with the same wall-thickness were close to those by the fixed conditions.

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